1. Field of the Invention
The present invention relates to suspension springs for vibrating piezoelectric plates, used for manufacturing resonators with low accelerometric sensitivity.
2. Description of the Prior Art
Piezoelectric plates used for manufacturing resonators are generally fixed to a base by means of metal springs often formed from a shaped nickel strip. These springs serve as mechanical filters and are consequently indispensible.
Under the effect of an acceleration, these springs are deformed which causes deformation of the piezoelectric plate which they hold. This deformation of the vibrating plate causes a variation in the resonance frequency of the resonator which is sufficiently high to exceed the admissible tolerances in certain devices. A known means of overcoming this drawback consists in providing for this frequency variation. The piezoelectric plate is then designed to resonate, in the absence of acceleration, at a frequency close to but different from the desired frequency and to resonate at the desired frequency for a given acceleration. Besides the difficulty which this frequency approach entails, this remedy is only valid for a given acceleration value and the resonance frequency will very rapidly be situated outside the tolerance limits for acceleration values which are too far removed from this particular value.
In order to overcome these drawbacks, the invention provides suspension springs of an original design, including at least two parts: one part intended to be fixed on the base of the resonator and a part intended to support the vibrating plate. The geometry of these parts as well as their special arrangement mean that the springs of the invention are deformed under the effect of an acceleration but only cause small deformation of the vibrating plate and consequently only a small variation in the resonance frequency, whereby the set tolerances can be complied with.